The atopic diseases consist of the triad of asthma, allergic rhinitis, and atopic dermatitis. These diseases share a common pathogenesis, involving inflammatory Th2-type cytokines and elevated IgE. Interestingly, they frequently present together in the same individual and family, suggesting common factors and mechanisms are involved in these diseases. Recent evidence has been accumulated to suggest that Th2-type CD4+ T cells play a triggering role in the activation and/or recruitment of IgE antibody-producing B cells, mast cells and eosinophils, i.e. the cellular triad involved in the allergic inflammation. However, the mechanisms underlying the preferential activation by environmental allergens of Th2 cells in atopic individuals still remain obscure. A likely candidate for such an initiating facor is the cytokine thymic stromal lymphopoietin (TSLP). TSLP is upregulated in the lungs of mice with airway inflammatory disease and humans with asthma. In addition, mice lacking TSLP responses fail to develop allergen-induced airway inflammation. Finally, TSLP is also induced in airway epithelial cells infected by respiratory viruses, suggesting a role for TSLP in these responses. TSLP action is not limited to the skin - it has also been implicated in allergic responses in the lung and the nose, thus making it a common element in atopic diseases. The experiments in this proposal will test this hypothesis by 1) analyzing the role of respiratory viru-induced TSLP in driving asthma using bronchial epithelial cells from healthy and asthmatic children, as well as animal model systems; 2) determine the role of TSLP in chronic airway inflammatory disease using a cockroach antigen model; 3) determine whether TSLP is a factor in the atopic march, where individuals with one allergic disease are more likely to develop a second. The information gained from these studies will be critical in determining the role of TSLP in allergic lung disease, and will provide insight into whether TSLP is a therapeutic target for their treatment.